This invention relates to continuous casting machines and in particular to a thermocouple for monitoring the temperature of the mold in a continuous casting machine.
Continuous casting machines are well known in the prior art and include a mold made up of two essentially parallel wide walls and two essentially parallel narrow walls which cooperate to define a casting passage of rectangular cross section. The size of the continuous slabs formed by the continuous casting method may be up to 12 inches thick and 100 inches wide. The mold is surrounding by a water jacket which cools the mold. Conventionally the mold walls are made of copper plates having high thermal conductivity to permit effective cooling of the mold by water. The back surface of the mold walls which are surrounded by the water jacket are generally grooved to insure more efficient cooling by the cooling water which flows over the back surfaces of the mold walls.
Continuous casting molds are generally arranged vertically whereby the molten metal, which is at a temperature in excess of 2000.degree. F. as it enters the mold, is cooled by the mold so that a skin initially forms around the molten metal and forms a slab. The metal inside the skin will still be molten at this time.
Due to the initial weakness of its skin, the slab must be supported even after it leaves the mold. Thus, a series of support zones are arranged downstream of the mold for supporting the slab as it cools. The slab will progress to a position wherein the slab is cut into sections.
It is very important that the temperature of the mold be accurately monitored so that the mold temperature will not become too high. If the mold temperature becomes too high, a situation called "break-out" occurs in which the skin of the slab, as it emerges from the mold, is too thin and will rupture or break whereby the molten metal inside the slab will pour out through the break and run down through the casting equipment. If this occurs, the entire casting apparatus must be shut down and repaired, thus resulting in costly repairs as well as down time of the continuous casting equipment.
In order to insure that the mold temperature does not become too high, thermocouples have been used in the past to monitor the mold temperature. These thermocouples are sometimes called sticker detectors and are used to sense the temperature of the mold which is at or near the temperature of the slab skin. If an excessive temperature is sensed, the mold is shut down or other action is taken to prevent a break-out from occurring.
Prior art continuous casting mold temperature sensors generally have comprised thermocouples which were immersed in the cooling water inside the water jacket and which contacted the back surface of the mold over which the cooling water was circulated. Thus, such thermocouples have been referred to as "wet" thermocouples. Such thermocouples have commonly been constructed of constantan which is an alloy containing from 50% to 60% copper and from 40% to 50% nickel.
A problem with such prior art "wet" thermocouples has been that the constantan thermocouple tips tend to become contaminated by the build-up of calcium or other impurities contained in the water. This build-up of deposits results in inaccurate readings and potential electrical shorts of the thermocouple, thus resulting in break-outs. Build-up of deposits could also result in a slower response time of the "wet" thermocouple and the resultant occurrence of break-outs. Attempts have also been made to place the thermocouples inside the bolts which hold the mold walls or "coppers" to the water jacket. However such designs permitted water to leak out of the water jacket which problem was aggravated by the thermal expansion and contraction of the coppers.
It is therefore desired to provide a dry thermocouple for a continuous casting mold, thereby eliminating the possibility of contamination of the thermocouple, inaccurate and delayed readings of the thermocouple and break-outs.